The present invention relates to the regulation of internal combustion engine operation, and more particularly, but not exclusively, relates to controlling engine operation near the lean burn misfire limit.
In efforts to reduce harmful exhaust emissions from internal combustion engines, it has been discovered that exhaust pollutants, such as Nitrogen Oxides (NOx), generally decrease when a lean mixture of air and fuel is provided to the engine for combustion. U.S. Pat. Nos. 5,107,815 to Van Duyne and 4,562,818 to Kohama et al. provide representative examples of attempts to address harmful exhaust emissions.
Typically, lean burning operation of an engine is limited by misfiring, which results when the air/fuel mixture provided to the engine becomes too lean. Misfires generally undermine smooth, reliable, and efficient engine operation. Therefore, it is often desirable that the air/fuel mixture be regulated to provide a minimum of exhaust pollutants, while still reliably avoiding misfires.
One attempt to regulate the air/fuel mixture is based on the amount of oxygen detected in the engine exhaust stream with an oxygen sensor. Unfortunately, lean burn regulation in accordance with the amount of residual oxygen in engine exhaust is somewhat limited. Indeed, although the measurement of residual oxygen may be utilized to detect misfires under some circumstances, this approach is typically ineffective as an indicator of proximity to the lean burn misfire limit.
Also, oxygen sensors suitable for exhaust gas measurement are generally too inaccurate to maintain engine operation close to the lean misfire limit. In addition, oxygen sensors tend to drift with age and are susceptible to humidity variations, which often limits effectiveness in lean burn control systems. Because of these constraints, lean burn systems based on an oxygen sensor ordinarily select an operating point that is not as lean as would otherwise be desired.
Thus, an alternative approach to controlling lean burning engines is needed. The potential pollution reduction from an improved lean burn control of large, gaseous-fueled internal combustion engines, such as the type used to drive electric power generators, would be particularly advantageous. The present invention satisfies these needs and provides other significant advantages.